In a mobile communications system, the location of a mobile terminal is always monitored in order to determine in which location registration area the mobile terminal is located geographically. This is done mainly for the purpose of activating the service for that mobile terminal. Every time the mobile terminal moves from one area to another, the mobile terminal transmits a notice to the network, and the network stores the location information transmitted from the mobile terminal in an appropriate database.
The location information is stored and managed in an HLR (Home Location Register). Services for a mobile terminal, including transmission of a call to the mobile terminal, are activated based on the location information stored in the HLR. On the other hand, there are two types of methods for managing a subscriber profile, which is information about a subscriber, such as contract terms and registered services.
The first method is referred to as an HLR method. In the HLR method, the subscriber profile is stored only in the HLR. Such subscriber profile is read out of the HLR storage every time it is required. The second method is referred to as a VLR (Visitor Location Register) method. In the VLR method, the subscriber profile is transmitted to a database furnished in the corresponding area in which location registration has been made. Currently, the VLR method is the mainstream in mobile communications systems.
FIG. 1 illustrates a conventional mobile communications system. Multiple radio base stations 10a, 10b, . . . , are connected to the associated radio control station 12b. Similarly, radio base stations 10i, 10j, . . . , are connected to the associated radio control station 12k. Each radio base station defines its service area. The radio control stations 12a, 12b, . . . , 12j, 12k . . . are connected to associated switching stations (or switches) 14a, 14b, etc. The switching stations 14a, 14b, . . . are connected to a home location registration station (or a home location registration apparatus) 16.
The home location registration station 16 is provided with an HLR 17. Each of the switching stations 14a, 14b, . . . , is provided with a VLR 15. HLR 17 is logic and database furnished in the home location registration station, and used to manage the location of a mobile terminal. VLR 15 is logic and database furnished in the switching station, and used to manage the location of a mobile terminal. In this specification, both HLR 17 and VLR 15 represent logical functions, and they are not always consistent with the node names (HLR, VLR) used in a particular system, such as GMS.
There is a tendency extending back over recent years toward reducing the area size of a base station (i.e., location-registration area) for the purpose of dealing with an increase of subscribers along with the progress of mobile communications services. By making the location-registration area as small as possible, the load on the database of the switching station or the VLR 15 managing that area can be reduced when the network calls a mobile terminal located in that area.
However, reducing the location-registration area size inevitably leads to an increase of the number of times conducting location registration, which is a procedure taken when the mobile terminal moves to a new area to inform the network of the new location. Since HLR 17 manages a huge number of mobile terminals, the HLR 17 suffers from a heavy load when the traffic for location registration increases.
With the VLR method, upon updating the location information of a mobile terminal, HLR 17 downloads the subscriber profile and transmits it to the VLR 15 that controls the base-station area into which the mobile terminal has moved. This download and transmission procedures greatly affect the network. For example, if a subscriber moves by train across several areas under different base stations, location registration is carried out and the subscriber profile is downloaded onto the associated VLR 15 every time the train moves into a new area. The subscriber profile is used to activate a service, such as relaying a call from a caller to that subscriber or transmitting a call from the subscriber to a third person. If no service is activated in the areas under the control of the VLR 15 that has received the subscriber profile, that subscriber profile will not be used
FIG. 2 illustrates the conventional location registration. In this example, a mobile terminal 20 moves across location-registration areas #a, #b, #c and #d, and a service is activated in area #d. The mobile terminal 20 transmits a location registration request every time it moves into the new area. The associated VLRs 15a, 15b, 15c, and 15d carry out a location registration process with respect to the HLR 17 to update the location of the mobile terminal 20 (as indicated by the dashed bi-directional arrows), and a download process of the subscriber profile (indicated by the bold bi-directional arrows).
The mobile terminal 20 does not activate a service in location-registration areas #a, #b, and #c, and if no network activation occurs in these areas, the subscriber profile transmitted to VLRs 15a, 15b and 15c becomes futile, and unnecessary traffic is produced.
With the conventional technique, subscriber profiles that may not be used in many cases are downloaded frequently, which not only causes the network traffic to increase, but also increases the load of database processing at HLR 17 and VLRs 15a, 15b, 15c and 15d. 